The reader is presumed to be familiar with commonly used communications network terminology and protocols. For general background information, the reader is referred to Roger L. Freeman, Practical Data Communications, John Wiley & Sons, New York, 1995, and the applicable networking standards published by standards bodies such as the Institute of Electrical and Electronic Engineers (IEEE) and the International Standards Organization (ISO), and the Bellcore (now Telcordia) SONET Generic Requirement documents (GRs).
Modem data communication networks often include multiple links or data paths between two or more network elements depending on the network topology. These links are typically monitored for failure and performance degradation by a network management system using a network management protocol. The network management system monitors the network for failure or signal degradation and initiates restoration of the network by, for example, selecting a different physical link to carry the signal.
Depending on the transmission format, the performance of links in a network may be determined by: 1) the transmission signal power received at the monitoring network element, 2) the ability of the monitoring network element to recover bit or frame synchronization with the data stream, or 3) receipt of specific expected data patterns. For network elements using data patterns to monitor performance, the data patterns may be defined in an overall time division multiplexing (TDM) framing format such as Synchronous Optical Network (SONET), or as “hello” or, “handshake” packets typically employed by packet-based data communications networks.
For networks using transmission codes (e.g., block codes), the rate that transmission code violations are received is another indication of the performance of a link. Transmission codes are typically used in communication systems to provide error detection and correction capability through the addition of systematic redundancy at the transmit end of a link such that errors caused by the transmission medium can be corrected at the receiver by means of a decoding algorithm. The amount of redundancy is typically dependent on the type of code selected and the level of error correction capability desired. Although many modem networks use transmission code violations to provide error detection and correction, these conventional systems do not use transmission code violations to trigger network restoration and protection.
Accordingly, there is a need for a system and method of monitoring a network for transmission code violations, and to trigger network restoration and protection based on the number of transmission code violations. It is desired that such a system and method have low overhead and low cost so that it may be easily integrated into existing communications systems and network topologies.